Equating a Car Alternator with the Generated Voltage Equation By Ervin Carrillo Senior Project ELECTRICAL ENGINEERING DEPARTMENT California Polytechnic State University San Luis Obispo 2012 © 2012 Carrillo TABLE OF CONTENTS Section Page Acknowledgments ......................................................................................................... i Abstract ........................................................................................................................... ii I. Introduction ........................................................................................................ 1 II. Background ......................................................................................................... 2 III. Requirements ...................................................................................................... 8 IV. Obtaining the new Generated Voltage equation and Rewinding .................................................................................................................................... 9 V. Conclusion and recommendations .................................................................. 31 VI. Bibliography ........................................................................................................ 32 Appendices A. Parts list and cost ...................................................................................................................... 33 LIST OF FIGURES AND TABLE Section Page Figure 2-1: Removed drive pulley from rotor shaft [3]……………………………………………. 4. Figure 2-2: Circuit components located under the cover of the alternator [3] ........................................ 4. Figure 2-3: (a) Stationary carbon brushes. (b) Rotating slip rings located on the end of the rotor [3].5. Figure 2-4: Rotor removed from alternator [3]……………………………………………………..5. Figure 2-5: Picture of Stator [3]…………………………………………………………………….5. Figure 2-6: (a) The alternator’s diode rectifier. (b) Schematic of the rectifier circuit [3] ........................ 6. Figure 4-1: DC motor coupled with car alternator .................................................................................... 12. Figure 4-2: Rotor with Marked North and South Poles ........................................................................... 15. Figure 4-3: Stator Internal Diameter (ID) and Rotor Diameter (D). ...................................................... 16. Figure 4-4: Machine Air-gap.......................................................................................................................... 16. Figure 4-5: Stator Core-Length. .................................................................................................................... 17. Figure 4-6: Rotor Radius to Air-gap ............................................................................................................ 18. Figure 4-7: One of the Three-phase Windings on the Rotor .................................................................... 20 Figure 4-8: Two different perspectives of the angular rotor Pole-pitch of a car alternator. [1]. ........ 21. Figure 4-9: The mechanical angle covered by a single coil, measured in degrees( ). The coil-span angle could be measured using a circular protractor. ................................................................훉퐦 ................ 22. Figure 4-10: Re-wounded single-phaseof Stator with the maximum number of windings that fit in its slots. .................................................................................................................................................................. 29. Table 4-1: Results of Open Circuit Test ........................................................................... 13. Table 4-2: The Five Fifferent Component of Equation 5.............................................. 14. Table 4-3: The Four Physical Dimensions of the Alternator that need to be measured ............................................................................................................................................... 14. Table 4-4: Measured Physical Parameters ........................................................................ 18. Table 4- 5: Result of Applying Equation 16 at Various Input Field Currents.. ........... 26. Table 4-6: Phase-voltage at 12 volts DC output .............................................................. 27. Table 4-7: Field Current at 12 Volts DC output ............................................................. 28. ACKNOWLEDGMENTS This project would have not been possible without the help and support of various individuals. I would like to give special thanks to my advisor Dr. Taufik for all his advice and guidance. I would also like to thank the Electrical Engineering Department Faculty at Polytechnic State University, San Luis Obispo, who provided us with the knowledge and facilities to the fulfill this project. I would also like to acknowledge Yuri Carrillo, my senior project partner/sister, for all her help and contributing knowledge. Lastly, I would like to thank my father Crisanto Carrillo who helped us couple the car alternator to the dc motor coupling. i ABSTRACT The following report presents the first key steps required in effectively retrofitting a car alternator into a low rpm generator for use in small-scale renewable energy sources. A car alternator is run through an open circuit test and taken apart in order to measure its physical dimensions. The data collected are then used to determine machine parameters required in the alternator’s generated voltage equation. The appropriate number of stator windings for a given lowest rpm may then be determined using the equation. The alternator’s stator is then rewound and remounted in the alternator to demonstrate whether the low rpm can be achieved. A Toyota alternator is retrofitted in this project which provides the step by step procedure on obtaining the alternator parameters to be laid out; hence, may serve as a guideline for anyone attempting to retrofit a car alternator for low speed rpm applications. ii I. INTRODUCTION There has been a growing interest in applying sustainable energy solutions to the needs of people living in developing countries. In remote areas, where there exists no electrical grid due to its great expense, small energy harvesting systems are desired. One example of such a system is a small scale hydro generation system. The main constrain faced by small scale hydro generation is the low rpm requirement of 200rpm – 600 rpm. Unfortunately, the generators that are designed to operate at these low rpm are relatively expensive. The price of these generators is usually no lower than 100 dollars. The proposed solution to this problem is to retrofit a car alternator into a low rpm generator in a cost-effective manner. The problem faced by current retrofitting methods is that they require that a car alternator’s electromagnet rotor is replaced with a permanent magnet rotor [4]. Magnetic material can be difficult to find or expensive to buy in developing countries [4]. An alternative method to retrofitting a car alternator is to rewind the alternator’s stator. This paper provides an easy to follow guide on how to equate a Toyota car alternator to an equation. The equation will allow a person to more accurately determine the number of stator windings needed to reduce the rpm requirement of the car alternator. This paper also introduces a possible way of rewinding the stator. The information provided in this document may serve as a key first step in the retrofitting process of a car alternator into a low rpm generator. 1 II. BACKGROUND 2.1 Importance of Relating Car Alternator to Equation Presently, there is no clear and direct guide available that relates electromagnetic theory to the physical parameters of the commonly used AC machine known as the car alternator. The information that an individual, such as a college student, has access to through the internet or textbooks only provide the following: a basic understanding of AC machines concepts, or steps on how to change a component in a car alternator without a clear reason. There are various professors and students involved in renewable energy projects, where a clear correlation between a car alternator’s physical components and electromagnetic theory would help them appropriately retrofit an alternator to their desired requirements. Therefore, this paper will provide a clear guide on how to relate a car alternator components, and dimensions to the parameters of the Generated Voltage Equation. 2.2 The Generated Voltage Equation It is well known that a voltage can be induced by mechanically rotating a magnetic field past a set of wound coils. All ac machines that convert rotational energy into electrical energy make use of that concept. The equation below show the relation between the induced voltage in rms, number of windings, rotational speed, and flux of the rotating magnetic field. 2 2-1 ퟏ 푬풓풎풔 ≈ � � 흎풎풆풌풘푵풑풉흋풑 √ퟐ 풓풎풔 푬 ≡ 풍풊풏풆 풕풐 풏풆풖풕풓풂풍 풓풎풔 풗풐풍풕풂품풆 풑풓풐풅풖풄풆풅 풃풚 풂풄 풎풂풄풉풊풏풆 흎풎풆 ≡ 풆풍풆풄풕풓풊풄풂풍 풇풓풆풒풖풂풏풄풚 풘 풌 ≡ 풔풕풂풕풐풓 풘풊풅풊풏품 풇풂풄풕풐풓 풑풉 푵 [ ] ≡ 풏풖풎풃풆풓 풐풇 풕풖풓풏 풘풊풅풊풏품풔 풑풆풓 풑풉풂풔풆 풐풏 풔풕풂풕풐풓 풑 흋 ≡ 풂풊풓 − 품풂풑 풇풍풖풙 풑풆풓 풑풐풍풆 푾풃 It must be noted that the equation 2-1 is only valid when the given ac machine is operated in normal steady state. Since, the aim of this paper is to parameterize a car alternator that will be operated at steady state; equation 2-1 can be applied. Equation 2-1 is the basis of the whole paper. 2.3 The Key Components of a Car Alternator All car alternators